At present, filters, cyclones, or electrical methods, such as electric filters or an ion blow method, are used in gas purification systems and for separating particles from a gas flow. Methods and devices for separating particles or drops from a gas flow are e.g. known from DE 1471620 A1 and DE 19751984 A1.
Air purifiers that are currently being used have moved away from the conventional method of using filters in order to mechanically extract unwanted particles from air. Such conventional filtration systems suffer from the disadvantages that the air flow has to be limited to a slow flow stream and that the filter has to be periodically removed for cleaning. In addition, it is not possible to achieve good cleaning results with the known techniques, when the particles have a diameter in the range between a nanometer and a few dozen nanometers.
The operation of the cyclones is based on the decrease in the gas flow speed so that the heavy particles in the gas flow fall down into the collection organ. Cyclones are thus applicable for separating heavy particles.
In electric filters, the separation of particles from gas is carried out onto collection plates or to interior surfaces of pipes. The speed of the flowing gas in electric filters has to be generally under 1.0 m/second, manufacturer's recommendations being about 0.3-0.5 m/second. The reason for a small gas flow speed is that a higher flow speed releases particles accumulated onto plates, thus decreasing reduction efficiency considerably. The operation of electric filters is based on the electrostatic charge of particles. However, it is challenging to electrically charge particles in the nanometric category. In addition, all materials are not charged electrically. Low gas flow speed has to be used also because of the cleaning stage of the collection plates. When cleaning the plates, a blow is directed to the plates, releasing the collected particle material. The intention is that only the smallest possible amount of particle material released from the plates during the purification stage would get back to the flowing gas. With a small gas flow speed it is possible to achieve tolerable particle passing throughs.
Further, electric air purifiers exploit the properties of charges in ionised gas and use electrostatic means to extract the charged particles from a directed airflow. This method of extraction improves efficiency not only in terms of overall amount of particles being extracted but also the types of particles. An air purifier would typically exploit the properties of positively or negatively charged particles where an electric field would interact with these charged particles. The charged particles would respond to the electric field and be pulled towards the ion blow onto a collection surface.
Document EP 1165241 B1, for example, discloses a method and device for separating materials in the form of particles and/or drops from a gas flow, in which method the gas flow is directed through a collection chamber the outer walls of which are grounded, and in which high tension is directed to the ion yield tips arranged in the collection chamber, thus providing an ion flow from the ion yield tips towards the collection surface, separating the desired materials from the gas flow. It is characteristic of the invention that the collection surface conducting electricity are electrically insulated from the outer casings, and that high tension with the opposite sign of direct voltage as the high tension directed to the ion yield tips is directed to the collection surface. According to an embodiment of the invention the electrical insulation is made of ABS, and the surface conducting electricity comprises a thin chrome layer arranged on the insulation layer. The ion yield tips are arranged in rings, with the help of which the distance between the ion yield tips and the collection surface is made shorter. Thus, some particles contained in the slow gas flow do not pass through the ion beams, but instead between the fastening rod and the ion yield tips.
In view of the foregoing, it would be beneficial to provide a method and a system further improving reduction efficiency. The system should be capable of being manufactured in industrial scale.